This invention relates to an ignition timing controller for an internal combustion engine and more particularly to an improved timing controller that controls the timing of the engine in response to abnormal changes in engine speed as well as to normal changes in engine speed.
It is well known that the ignition systems for internal combustion engines operate to control the spark advance in response to engine speed. Normally, the spark advance is held at a fixed degree of advance during cranking, idle and for a certain phase of low speed operation. The spark is advanced along a curve as the engine speed increases up until a predetermined maximum degree of spark advance. This maximum spark advances normally occurs before wide open throttle of the engine. The spark advance is then held constant as the engine speed continues to increase up to its maximum. Although the exact configuration of the spark advance curve may vary from that as aforedescribed, the general principles apply.
Although spark advance mechanisms of the type as aforedescribed are extremely effective, their effectiveness deteriorates under certain abnormal conditions. For example, if the engine speed is suddenly increased or, more importantly, decreased, there is a likelihood that the normal spark advance curve will not provide the adequate spark timing and poor running or, in extreme instances, stalling may occur. Therefore, systems have been proposed to alter the spark advance curve in response to such external abnormal conditions. For example, reference may be had to U.S. application Ser. No. 229,924, entitled, "Control Means Of Internal Combustion Engine For Marine Propulsion", filed Aug. 8, 1988 in the made of Kazumasa Ito and also to U.S. application Ser. No. 247,748, entitled, "Spark Timing Controller For Spark Ignited Internal Combustion Engine", filed Sep. 21, 1988 in the name of Itsushi Hirukawa, both of which applications are assigned to the assignee hereof, for ignition systems having arrangements to alter the spark advance curve in response to these abnormal conditions. Although these devices certainly act significantly to improve the performance under, extreme conditions and will insure against stalling, these devices are of the generally "on" or "off" type. That is, if an abnormal condition is sensed, the spark advance curve is modified whereas under, normal running conditions no modification occurs. However, the degree of modification which may be required can vary with respect to the severity of the abnormal condition.
It is, therefore, a principal object of this invention to provide an improved ignition timing control for a spark ignited internal combustion engine wherein the normal spark advance is modified in response to the severity of an abnormal condition.
It is a further object of this invention to provide an improved arrangement for controlling the spark timing of an internal combustion engine in response to the magnitude of sensed abnormal conditions.
It is a further object of this invention to provide an improved ignition timing control for an engine that is responsive to all running conditions.